1. Field of the Invention
This invention relates to novel water-insoluble silica-containing pigments for use in coloring plastic articles. More especially, this invention relates to water-insoluble silica-containing dye pigments made by a process comprising hydrolyzing a water-soluble dye in the presence of an organooxysilane and drying the resultant gel.
2. Discussion of the Prior Art
Only pigments or dyes which are insoluble in water are suitable for coloring plastic articles, since they cannot be dissolved out of the polymer upon treatment with cold or hot water. The coloring of varnishes and lacquers can, for the same reasons, be performed only with water-insoluble dyes or with pigments.
Furthermore, it is often desirable to give plastic moldings or even varnishes and lacquers a dull appearance. For this purpose, chalk is generally added to the raw materials as a dulling agent. Chalk has the disadvantage, however, that it often brings about an undesirable increase in the bulk weight of the polymer, thereby increasing its density.
The problem therefore existed of converting water-soluble dyes to an insoluble form which, if possible, would at the same time also produce a dulling effect.